Method of making arsenical compounds



Patented Dec. 15, 1931 UNITED STATES PATENT OFFICE HARRY B. GOODWIN, OF GRAND JUNCTION, COIDRADO, ASSIGNOR TO THE LATIMER- METHOD OF MAKING ARSENICAL COMPOUNDS No Drawing.

Zinc arsenite has been found to have considerable value as an agricultural insecticide, however its wide spread introduction has been hindered by lack of commercial methods for its production. While soluble salts of zinc and an alkaline arsenite may be reacted together successfully, such procedure is not feasible from the commercial standpoint on account of the high costs involved. It has been proposed to utilize arsenious oxide as a starting material, this being boiled with Water to bring into solution, and then with the addition of amounts of zinc oxide, boiling is further continued, until by degrees the zinc oxide is worked up in reaction to form zinc arsenite (United States patent to Vreeland 1,296,344). Such method however requires excessively long boiling, both for initially bringing the arsenious oxide sufiiciently into solution, and then more especially for attaining reaction with the zinc oxide, and as a result, the entire process is so inefiicient and time consuming as to be undesirable commercially. Moreover, it will be noticed that this procedure deals continuously with an acid solution, and this introduces further diiliculties in the way of practical procedure. A process of making zinc arsenite which will avoid such difficulties, and will be capable of operation in an efficient commercial manner is accordingly fundamentally important and highly desirable.

To the accomplishment of the foregoing and related ends, the invention, then, consists of the features hereinafter fully described, and particularly pointed out in the claims, the following description setting forth in detail of the invention, such setting forth howeve but one of the various ways in which the principle of the invention may be employed.

In proceeding in accordance with the invention, zinc oxide and arsenious oxide'are treated under suchconditions as to involve a non-acid aqueous medium, and a carrier promotive of reaction is employed.

As such, a mineral acid, in small proportions, ordinarily less than 1%, and preferably .1-.5% is employed. Of such mineral acids, sulphuric acid is particularly desirable.

Application filed July 23,

certain procedure illustrative 1928. Serial NO. 294,941.

being readily available generally. The operation is started by acidulating a given volume of Water, to an acidity for instance .1 to .5%. Then a small proportion of zinc oxide is added, for instance .1.5%. Arsenious oxide and further amounts of zinc oxide are added. up to the total requirements of the reaction. Since the acid added is at once neutralized by the first charge of zinc oxide, special acid proof receptacles are not required, and operations may be carried on in Wooden vats, preferably equipped with effective stirring mechanism. Heat is advantageously applied, artioularly after the initial introduction ofizinc oxide, and such heat as is desirable may be effectively had by simply turning live steam into the bottom of the tank. This procedure in fact can at the same time also afford agitation.

As an illustrative example: 1222 gallons of water are run into a suitable wooden tank equipped with stirring mechanism, and to this is added 19.5 pounds of sulphuric acid of 655 B. The acidity of the water is then about 163%. Then 15 pounds of zinc oxide is added, and live steam is turned into the tank and agitation started. The necessary amount of zinc oxide is added, also the arsenious oxide, the zinc oxide being in amount of 14.85 pounds and the arsenious oxide in the amount of 1000 pounds. The amounts of these is dependent upon the actual zinc and arsenic content, this being readily checked by analysis. The relation between the volume of water and the total weights of the oxides may vary considerably but in gene al the smaller amount of water however tends to slow the reaction, while on the other hand more water can be used with favorable results. In this case, the 1222 gallons of water to 2485 pounds of oxides is further quite satisfactory on account of the consistency of the suspension obtained, this being a slurry capable of being readily handled by pumping. The addition of the zinc oxide and the arsenic oxide requires no particular attention in the way of slow and gradual supply, and the last addition may be made merely as the solution comes to a boil. By admitting steam more rapidly, the time can be shortened. In about pumped ofi to a filter press.

one-half hour to one hour the reaction is completed, and the solution may then be may then be washed and dried, and finally pulverized. 7 An average analys s of such product shows:

Total arsenic as arsenious oxide, 40.65%. Soluble arsemc as arsenious oxlde, 56%.

' 7 Volume of powder, over 100 cu. in. to the bound.

The filtrate from the filter press may be turned to the next batch, water being added thereto to bring up the volume to the total amount desired for the run, whereupon 7 V the degree of fluffiness obtainable where op-' itmay be acidulated, and the procedure repeated. V I V V A satisfactory zinc arsenite should contain between 10 and 41% total arsenious oxide, and not over 1% of soluble arsenic, and its physical state shouldbe that of a light fluffy powder. ihe present process affords par ticularly satisfactory, results as to the charact'er of the powder, being much superior to erations are carried on in acid medium. It Wlll be seen furthermore that tlns'procedure affords ethcient and rapld. convers1on,-em-

ploying crude materials of practically no solubility to start with and at the same time, a the materials may be handled in such manner oxide The press cake 7 as to take full advantageof operations in V slurry form. I V

.Other modesof applying the principle of the invention may be employed, change being made as regards the details disclosed, pro- 7 of the following vided the steps stated in any claims,or the equivalent of'such, be employed, I therefore particularly point out and distinctly claim as my invention V 1. A process of making zinc arsenite, which comprises treatmg zinc oxide with arsenious oxide anda mineral acid,-'in aqueous suspension. V

. 2. A process of making zinc arsenite, which comprises treatmgzinc oxide with arsenious oxide and .1-.5% sulphuric acid, in aqueous 7 suspension.

3. A process of making zinc arsenite, which comprises adding a small amount of zinc oxide to acidulated water, then adding arsenious oxide and further zinc oxide and heating.

4. -A process of making zinc arsenite, which comprises adding sulphuric acid to water to V .1.2% acidity,- then adding .1.5% zinc oxide, then adding arsenious oxide and further zinc oxide and heating.

5. process of making zinc arsenite, which comprises adding 195 pounds of sulphuric of water, adding 15 acid to 1222 gallons 1 pounds ofzinc oxide, addinglOOO pounds of 'a-rs'enious oxide and 1485 poundscof zinc oxide, and heating and agitating.

6. Aprocess ofmaking zinc arsenite, which I i comprises treating zinc ox1de with arsenic 

